Enhancement of the photoacoustic effect during the light-particle interaction.

Exogenous photoacoustic contrast agents such as gold nanoparticles are widely utilized in photoacoustic imaging. Enhancing the photoacoustic performance of gold nanoparticles is pivotal for improving the quality and expanding the application scope of photoacoustic imaging. In this work, the photothermal and photoacoustic responses of gold nanospheres surrounded by water excited with a pulsed laser are obtained via a two-temperature model. The interplay between pulse duration and interface thermal resistance and its effect on the photothermal and photoacoustic performances are uncovered quantitatively. The results reveal that, as the pulse duration decreases, increasing the interfacial thermal conductivity can substantially enhance heat transfer between the gold nanosphere and the surrounding water. However, this approach does not effectively enhance the photoacoustic performance. Interestingly, when increasing the thermal conductivity, it was found that there is an optimal pulse duration within the range of 10 ps-10 ns. Employing an incident pulse laser with this optimal pulse duration can maximize the enhancement of the photoacoustic signal.

Multi-index control strategy from cement calcination denitration system: a model predictive control method for combined control of nitrogen oxide and ammonia escape.

The cement industry is one of the main sources of NOx emissions, and automated denitration systems enable precise control of NOx emission concentration. With non-linearity, time delay and strong coupling data in cement production process, making it difficult to maintain stable control of the denitration system. However, excessive pursuit of denitration efficiency is often prone to large ammonia escape, causing environmental pollution. A multi-objective prediction model combining time series and a bi-directional long short-term memory network (MT-BiLSTM) is proposed to solve the data problem of the denitration system and achieve simultaneous prediction of NOx emission concentration and ammonia escape value. Based on this model, a model predictive control framework is proposed and a control strategy of denitration system with multi-index model predictive control (MI-MPC) is built based on neural networks. In addition, the differential evolution (DE) algorithm is used for rolling optimization to find the optimal solution and to obtain the best control variable parameters. The control method proposed has significant advantages over the traditional PID (proportional integral derivative) controller, with a 3.84% reduction in overshoot and a 3.04% reduction in regulation time. Experiments prove that the predictive control framework proposed in this paper has better stability and higher accuracy, with practical research significance.

On Thermal Insulation Properties of Various Foaming Materials Modified Fly Ash Based Geopolymers.

Geopolymers can be used as a thermally insulated material because of their considerable porosity, whereas the combined effect of various modifying agents on their heat-insulating properties remains unexplored. Here, orthogonal experiments were carried out to evaluate the thermal insulation performance of fly ash geopolymer modified by phenolic resin, silica aerogel, and hydrogen peroxide. Moreover, variance analysis and range analysis were applied to estimate the influence of modifying agents on the thermal insulation performance of the geopolymer. The results demonstrate that the thermal conductivity of fly ash geopolymer significantly reduces (from 0.48 W/m·K to 0.12 W/m·K) due to the combined effect of the three modifying agents. Based on the variance analysis and range analysis, the optimum thermal conductivity ultimately reaches 0.08 W/m·K via a best composition scheme of the three modifying agents. Moreover, phenolic resin can facilitate the formation of a network structure and increase the porosity of micron pores (>1 µm). Hydrogen peroxide can be decomposed into O2 in an alkaline environment and leave large-diameter pores (>1 µm) during curing. Some silica aerogel is embedded in the geopolymer matrix as microspheres with extremely low thermal conductivity, whereas the rest of the silica aerogel may react with the alkali activator to form water, and subsequently leaves pores (>1 µm) after evaporation of water during the curing. In addition, a newly modified Maxwell-Euchen model using iterative calculation and considering the Knudsen effect (pores of micron or even nanometer scale) is proposed and validated by the experimental data. The foamed geopolymer in this research can be used as a reference for building insulation layer design. This research unravels phenolic resin-, silica aerogel-, and hydrogen peroxide-influenced thermal insulation mechanisms of geopolymer that may have impacts on deployment of a thermally insulating material in the construction field.

Effect of Anionic Polyacrylamide Polymer on Frost Heave Mitigation and Its Implication for Frost-Susceptible Soil.

Seasonally frozen ground regions occupy approximately 55% of the exposed land surface in the Northern Hemisphere, and frost heave is the common global problem in seasonally frozen soil areas. Frost heave induces uneven deformation of ground and damages railways, road paving, and buildings. How to mitigate frost heave is the most important technical issue in this field that has provoked great interest. Here, using freezing experiments, we investigate the effect of anionic polyacrylamide (APAM) polymer on frost susceptible soil. The results demonstrate a so-far undocumented inhibition of frost heave by APAM in freezing soil, namely APAM (tested at concentrations from 0.0 wt% to 0.60 wt%) slows down the frost heave by a factor of up to 2.1 (since 0.60 wt% APAM can decrease frost heave from 8.56 mm to 4.14 mm in comparison to the control experiment). Moreover, it can be observed that the maximum water content near the frozen fringe decreased from 53.4% to 31.4% as the APAM content increased from 0.0 wt% to 0.60 wt%, implying a mitigated ice lens growth. Hydrogen bonding between APAM and soil particles triggers an adsorption mechanism that accumulates soil particles, and thus can potentially inhibit the separation and growth of the ice lens. Moreover, the residue of APAM due to hydrogen bonding-induced adsorption in the pores of granular media may narrow seepage channels (capillary barriers) and provide an unfavourable condition for water migration. The use of APAM can also increase the viscosity of the solution, which causes a greater water migration resistance. This research provides new insights into APAM-influenced frost heave (introducing APAM into the soil can induce bridging adsorption between APAM polymer segments and a particle surface), can enable engineers and researchers to utilise chemical improvement design and to consider suitable actions (e.g., by injecting APAM solution into a frost susceptible soil or using APAM-modified soil to replace the frost susceptible soil) to prevent frost heave from having a negative impact on traffic roads and buildings in cold regions.